Corrosion resistant coated steel



Patented Aug. 31, 1948 umro STATES CQRBOSION RESISTANT COATED STEELAlbert A. Schilling, Stratford, and Walter L.

Finlay, Fairfield, Conn., assignors to Remington Arms Company, Inc.,Bridgeport, Conn, a corporation of Delaware -N0 Drawing. ApplicationJune7, 1944,

Serial No. 539,184

2 Claims.

The present invention relates, in general, to a method of improving thecorrosion resistance of metallic articles, and, in particular, steelammunition components and contemplates a novel coating on steelcartridge cases and shot shell heads comprising the combination of aphosphate coating and a furan resin with or without a suitable wax.

The art of forming protective coatings on steel cartridge cases andsimilar steel ammunition components is well developed. The so-calledParkerite or Bonderite processes of rendering steel surfaces corrosionresistant are characterized by the use of a phosphate coating which inconjunction with a suitable wax overcoat protects the steel surfacesfrom corrosion when ex posed to moisture, and, in particular, salt wateror salt spray, and from the electrolytic action set up between adjacentdissimilar metals, as, for example, betweenv the gliding. metal of a'cartridge primer and the steel of the cases or the. copper coating of abullet and the steel of the case.

The Parkerite and Bonderite processes are described in greater detail inUnited States patents, Nos. 1,167,966, 1,842,085 and 2,303,242.

It has been discovered, however, that the corrosion resistance of steelsurfaces, and, in particular, steel cartridge cases having a Parkeriteor Bonderite undercoating can be advantageously enhanced by theapplication of a film or overcoat of a furan resin. The term furan resinas hereinafter used will be understood to include the resins of furfural(furfuryl aldehyde) and furfuryl alcohol. The resins of furfural andfurfuryl alcohol are widely used in industry, and, in general, aremanufactured by the admixture of the furfuryl aldehyde or alcohol and acatalyst, such as a small amount of an acid, with or without heat. Theresins, and, in particular, the resin of furfuryl alcohol are attractivefrom a cost standpoint, possess appreciable heat resistance and form ahard, relatively non-brittle, infusible, water repellent coating, andhave been found especially suited for enhancing the corrosion resistanceof steel cartridge cases. The patents of Trickey et al., No; 1,665,235,April 10, 1928, Richardson, No. 1,682,934, September 4, 1928', andMeiler, No. 2,243,481, May 27, 1941, describe specifically severalmethods of forming furan resins which are particularly adapted tothepurposes of this invention.

Solutions of the furans having relative high acid concentrationsresinify with a vigorous reaction of almost explosive violence, whereassolutions of low acid concentrations provide spontaneous resinificationat room temperature. For coating steel cartridge cases in quantityproduction lots, 2. solution which is relatively stable at roomtemperature is preferred, setting being effected by the subsequentapplication of heat.

Moreover, it is necessary that a suitable acid be used which will notreact adversely with the Parkerized coating. An acid which has beenespecially suitable for the purposes of the present invention isphosphoric acid.

An example of a resinous composition which is fairly stable at roomtemperature and which has proven successful in coating Parkerized steelcartridge cases of small caliber, such as .22, .30 and .45 calibercases, is the admixture of a dilute solution of phosphoric acid(phosphoric acid and acetone in the ratio of 1.1) and furfuryl alcoholin the ratio of one part of the dilute acid to fifteen parts of furfurylalcohol.

Various methods of applying the resinous composition to the Parkerizedsteel cases may be used, for example, the cases may be dipped into a,bath of the resinous solution and then withdrawn and thereafter heatedto set the resinous coating. However, for small caliber relatively lightweight cases, the bulk or tumbling barrel method has proven successful.Thus, a small quantity of the resinous solution is put into a tumblingbarrel into which a lot of steelcases are dumped. After being thoroughlycoated the cases are removed from the barrel and, thereafter, a blast ofair at approximately 250 F. is directed onto the cases for substantiallyfive minutes. Each cartridge case is thereby provided with a resinouscoating which, when set up by the heat of the air blast, is smooth,water repellent, non-brittle and adherent.

For the larger and heavier caliber cases, such as Parkerized .50 calibersteel cases, the preferred method of coating is by dipping the casesinto a bath of the resinous solution, and then with.- drawing andheating the cases for substantially ten minutes at approximately 350 F.Due to the greater Weight and relatively large surface area of the .50caliber cases, a resinous coating formed by the bulk or tumbling barrelmethod is more apt to be cracked or scraped off at the corners of thecases, and hence is less satisfactory than coatings formed by dipping.

Suitable resinous coatings may also be applied to larger caliber casesby spraying the resinous solution onto hot Parkerized cases andthereafter providing additional heat to completely set the resin.

As mentioned above the resinous solutions may have different physicalcharacteristics such as viscosity and specific gravity depending uponsuchfactors as the type of catalyst used and the acid concentration ofthe solution. In this connection, it has been found advantageous toprovide a relatively non-viscous resinous solution for coating thelarger caliber cases in order'that the excess coating fluid will-quicklydrain off ofthe larger surface areas, and, in particular, from theinside of the cases. 1

To this end, a solution having substantially the viscosity of water isused and is prepared by adding a dilute solution of phosphoric acid andace-.

the solution separates into an upper layer of water and a lower layercomprising'a water in-' soluble resinification product of furfurylalcohol and phosphoric acid. This product is readily separable from thewater and thereafter dis 1 The re.

solved in three parts furfuryl alcohol. sulting product is relativelynon-Viscous and stable at room temperatures. A similar method of forminga partial resinification product as Well as an alternative method inwhich no acetone is used are described more fully in the Trickey et a1.and Richardson patents identified above. This relatively non-viscousresinification solution drains quickly from Parkerized .50 caliber steelcases which have been dipped therein. The coated cases are then heatedfor substantially ten minutes at 350 F. to set the resin. The resultingresinous coating is smooth, uniform, water im Moreover, the goodcorrosion inhibiting char' acteristics of furan resin coatings onPark-erized steel can, it has been discovered, be further enhanced by asubsequent coating of a hydrophobic material, such as a microcrystallinepetrolatum wax or a rust inhibiting oil. Cartridges so coated exhibit acorrosion resistance which is highly superior to waxed Parkerized steelcartridges and other known corosion inhibiting coatings.

It will be understood that, in order to obviate gumming up the barrelchamber and more especially the feed mechanisms of automatic firearms,the maximum thickness of a coating of wax on a Parkerized steel case islimited, and hence it is impracticable to enhance the corosionresistance of a waxed case by multiple coatings of wax.

However, it has been discovered that by coating a Parkerized steel casewith a furan resin and then applying anbvercoating of wax to the resin,a superior corrosion inhibiting surface is obtained. The coating ofresin is of itself Water impervious and is characterized by a lessporous structure than a microcrystalline Wax. The resin thus provides acorrosion resisting coating over the phosphate coating of the steel casewhich is less porous than either the phosphate coating or theovercoating of wax. Further, a wax coating is considerably softer thanthe furan resin coating and when used alone on Parkerized cases itssurface is more susceptible to scratches and indentations by abrasionand handling than are the harder resinous surfaces. It has also beenfound that the resin coatin provides a better bond between theParkerized coating of the steel case than wax.

The wax over the resin tends primarily to olfset any brittleness of theresin and provides a buffer for protecting the resinous coating from theforce of an inadvertent blow incurred during the handling of theresinous coated cases. The

wax overcoating is also used as a lubricant for the resin coated case.Moreover, by combining a corrosion inhibiting coat of resin with anovercoat of wax, the Wax coating may be relatively thin thereby avoidinggumming up the barrel chamber and feed mechanism of a firearm.

For the purposes of this invention, a suitable wax for coating furanresin coated steel cases jcomprisesthe compound known to the trade asSocony 2300, the characteristics of which are described in the UnitedStates patent, No. 2,298,844.

The wax coating is applied, in general, to the completed or loadedcartridge to provide an unbroken corrosion resisting buffer andlubricating coating on both the bullet and the resin coated case. Tothis end, a bath of the wax is provided comprising Socony 2300 dissolvedin a suitable solvent such as carbon tetrachloride. The cartridges arefirst immersed in the bath and then withdrawn, the wax taking the formof 'a substantially solid coating covering the entire cartridge. 7

Although the foregoing description has related to a method of coatingParkerized steel cases with a furan resin and wax, it will be understoodthat by selecting a resinous solution having a relatively non-vigorousreaction and one adapted to set up at relatively low temperatures loadedcartridges as well as empty cases may be successfully coated with acorrosion resisting furan resin coating and an overcoating of Wax.

What is claimed is:

1. A steel cartridge case having thereon a corrosion resisting coatingcomprising an undercoat of a phosphate, a coat of furfuryl alcoholresinified with phosphoric acid superimposed on said phosphate coat, anda thin exterior coat of wax, said wax coat being of a thicknessprocurable by deposition from a solution of wax in a solvent.

2. A steel cartridge case having thereon a corrosion resisting coatingcomprising a'phosphate coat directly upon said steel, a coat of furfurylalcohol resinified with a solution of acetone and phosphoric acid, and athin exterior coat of microcrystalline petrolatum wax, said wax coatbeing of a thickness procurable by deposition from a solution of wax ina solvent.

ALBERT A. SCHILLING. WALTER L. FINLAY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,665,235 Trickey et a1 Apr. 10,1928 1,781,507 Gravell Nov. 11, 1930 2,037,710 Ellis Apr. 21, 19362,047,957 Fletcher July 21, 1936 2,120,212 Curtin June 7, 1938 2,170,658Hucks Aug. 22, 1939 2,209,530 Mason July 30, 1940 2,323,333 Kauth July6, 1943 2,337,939 Sermattei Dec. 28, 1943 2,339,242 Abrams et a1. Jan.18, 1944 2,383,790 Harvey Aug. 28, 1945 2,418,935 Hutchinson Apr. 25,1947 2,423,872 Clipper July 15, 1947 FOREIGN. PATENTS Number CountryDate 9,92 Great Britain Feb. 18, 1915

